A futuristic look at the United States' defensive weapons system includes visions of space based lasers or particle beams able to direct their energy precisely and devastatingly upon any target. Concepts for the use of high energy particle beams for defense applications have been in existence for more than two decades, and extensive theoretical and experimental efforts have been performed, with many workers having contributed to the development and evaluation of the technology needed to produce these systems. Both ground based and space based systems have been studied. President Reagan has expressed a desire to place more stress on these efforts and the Defense Department has several programs that deal with these directed energy weapons.
One space based system that is currently being developed utilizes neutral particle beams. Contrasted to charged particle beams, neutral particle beams have several inherent properties that make them very attractive for space based applications, in particular, high energy neutral particles propagate in straight lines unaffected by the earth's magnetic field and have a very brief flight time to targets even at extended ranges. In addition, the neutral particles become high energy charged particles upon interaction with the surface of a target and penetrate deeply into the target, thus making shielding relatively ineffective. In the case of a nuclear warhead, these particles are capable of heating the nuclear material by fission processes, neutron generation, and ionization. For nonnuclear heavy targets, heating is produced by ionization, possibly producing kill by thermal initiation of the weapon's high explosive. Also, the response of targets to the high energy neutral particle beam is different for lightweight decoys and massive ICBMs which allow these beams to be utilized in a discrimination role where small kinetic kill vehicles are used to destroy the ICBMs once they have been identified.
Interest in space based application of these beams began when experiments, at the Los Alamos Clinton P. Anderson Meson Physics Facility (LAMPF), on the proton linear accelerator showed several orders of magnitude improvement in accelerator performance. Extensive measurements of beam properties at energies of 211 and 500 Mev showed that the energy spread of the beam was better than 0.5% and the emittance of the beam was better than 0.06 cm-mrad. Also, the LAMPF accelerator had been used to accelerate H.sup.- ions to energies above 100 MeV with their behavior being similar to that for protons. These achievement prompted Knapp and McNally to write a LANL report entitled "SIPAPU" in which they proposed a satellite-based high energy neutral hydrogen weapon; (see SIPAPU Report LA-5642-MS, Los Alamos National
Laboratory, July 1974). Their device is depicted schematically in FIG. 1, where an intense, high quality beam of H.sup.- ions is generated and accelerated to an energy of approximately 250 MeV. After acceleration, the beam is expanded and passed through final focusing and steering magnets. The diameter of the beam in the accelerator and beam transport sections is measured in mm, but after expansion the diameter of the beam is of the order of a meter. Therefore, the beam area has been increased by a factor of the order of 10.sup.6 and the current density has also been decreased by this same amount. This low current density beam is subsequently neutralized by stripping the weakly bound electron from the H.sup.- ion and the resulting hydrogen beam propagates toward the target unaffected by the earth's magnetic field. Both the system and the target must remain above approximately 250 kilometers during the engagement in order to minimize beam degradation due to collisions with residual gases in the atmosphere. However, this does not preclude the system being used in a pop-up fashion where the weapon is rocket borne for use in a fly-by or a fly-alone mode for either discrimination, target kill, or both.
Improvements in the state-of-the-art for intense high quality (high brightness) negative ion sources and light-weight efficient accelerators have been made. However, additional improvements are needed, and improvements in the state-of-the-art for compact lightweight power systems and for high current neutralizer techniques without excessive scattering are necessary before a device like this can be considered viable. Also, methods for neutral beam detection, signatures for closed loop tracking, for kill assessment, and techniques for rapidly steering the beam over larger angles are also needed.
Although, there are many practical issues to be considered, there does not appear, in principle, to be any inherent limitations that deem the device inviable. Many of the practical issues have been overcome and others are being addressed by the (Now SDIO/U.S. Army Strategic Defense Command (USASDC)) Neutral Particle Beam program. However, the current solutions for neutralization of the H.sup.- ion beam all have serious adverse systems implications.
After the H.sup.- beam has been accelerated, expanded, aimed, and focused on the target, it must be neutralized. This can be accomplished by a number of techniques. For example, photodetachment, plasma, or gas stripping have been considered. Photodetachment causes less degradation in beam quality and can result in the largest fraction of the negative ion beam being converted to a neutral beam. Unfortunately, extremely high energy CW lasers at wavelengths where these power levels are not currently available are required for this purpose, and even if they become available, they would probably be as large or as expensive and require as much prime power as the rest of the system. Since open ended plasma strippers with quiescent plasmas would cause less degradation in beam quality than a gas stripper, they also have been studied. But, the power requirement for the plasma stripper alone is equal to or greater than that for the rest of the system. Also, it is problematical that a sufficiently quiescent plasma could be produced. Therefore, considerable work both theoretical and experimental has been devoted and is being devoted to the development of a gas stripper. The important results of this work is summarized in FIG. 2 where the fraction of the initial beam which survives as H.sup.-, which is stripped to H.sup.o, and which is stripped to H.sup.+ is given as a function of the stripper thickness. Also, shown is the component of the H.sup.o beam which has not been elastically scattered (i.e., the useable part of the H.sup.o beam for targets at long ranges) and the component of the H.sup.o beam which has been elastically scattered (this is useful for beam sensing purposes).
As a result of this work a gas stripper is now included in current neutral particle beam weapon concepts. However, this is also an open system where gas escapes out the ends. Part of the gas, which escapes, expands back into the optical system where stripping collisions occur before the beam has been made parallel and these particles are therefore not directed toward the target. Part of the gas also escapes out in the forward direction where additional stripping collisions occur producing H.sup.+ particles which do not reach the target because of the effect of the earth's magnetic field. Thus, there is clearly a need for a better and more efficient way to neutralize the H.sup.- ion beam into H.sup.o neutral beams.
This need has been partially met by the teaching of Roberts, Havard, and Wilkinson in U.S. patent application Ser. No. 397,371 titled "Solid Stripper for a Space Based Neutral Particle Beam System." This neutralizer is shown in FIGS. 3, 4, and 5 where it may be seen to include a housing 10 which has a window opening 12 therethrough that is approximately 2 meters square. Inside housing 10, (see FIG. 4) reels 14 and 16 are mounted in a conventional manner with solid state stripper material 18 wound thereon. Reel 16 is a take-up reel and is motor driven by motor 20 (see FIG. 3) to move solid state material 18 past window 12 as the ion beam is passed through solid state material 10 as S illustrated in FIG. 5. Provisions are also made for discharging any charge accumulated on solid state material 18 by providing a conventional ground as it is taken up by reel 16.
In operations when the high energy H.sup.- beam is turned on, so is motor drive 20 which moves solid state stripper material 18 past window 12 at a linear speed of about 2 meters/sec. When the high energy H.sup.- beam is turned off, so is motor 20 for the take-up reel 16.
As can be seen, this solid state stripper is simple and requires negligible power. However, the thin foils are made of polyvinylidene chloride, mica, cellophane, and other similar materials, and the life time of such foils are limited to a few hundred mecro-ampere-hours. Also, the creation of such foils at optimum thickness even for 250 MeV H.sup.-1 beams at current densities of 10 .mu.amp/cm.sup.2 or greater is at best problematical. Such foils might be made as large as 0.3 meters but even these are very fragile. Foils thickness for lower energy applications such as antisatellite and discrimination need to be thinner and are very fragile even in much smaller sizes regardless of the material from which they are constructed.
Also, at the present time, only beam sensing diagnostics are planned after the beam has been expanded. These diagnostics are to determine to a high accuracy the direction in which the neutral particle beam has been pointed. These techniques assume that the beam profile is gaussian like and attempts are made to determine the beams centroid. A beam diagnostic technique is needed for measuring or determining both the power in the beam and the beams actual profile in a manner which does not attenuate, destroy, or distort the neutral particle beam.
Therefore, it is an object of this invention to provide a neutralization device that overcomes the defects of the Ser. No. 397,371 and extends its use to application at lower energies requiring thinner foils.
Another object of this invention is to provide a nonobstructing power meter that measures the output power of the weapon system without appreciably effecting or interferring with the use of the beam.
A still further object of this invention is to provide a device which can be used to obtain information on the spatial distribution of the current in the outgoing particle beam.
Additional objects and advantages of this invention will be obvious to those skilled in this art.